These investigations will focus on using molecular biological, biochemical, and genetic methods to elucidate how messenger RNA is degraded in bacteria. Particular attention will be devoted to RppH, a recently discovered RNA pyrophosphohydrolase that triggers the degradation of primary transcripts in E. coli by a previously unrecognized mechanism: the rate-determining conversion of the 5'-terminal triphosphate to a monophosphate. First, the features of RNAs that determine their susceptibility to decay by this mechanism will be identified. In addition, the characteristics of RppH that are important for its activity and the cellular factors that may influence such 5'-end- dependent RNA degradation will be examined. Finally, the contribution of this pathway to mRNA decay in other bacterial species will be explored. The results of these studies will provide important insights into a fundamental aspect of gene regulation that presently is poorly understood. This knowledge should be of value in clarifying a biological regulatory mechanism that can play a key role in bacterial pathogenesis.